1. Field of the Invention
The present invention relates to an osteosynthesis device with at least two bone screws, which can be secured to a vertebra of a spinal column; each bone screw has a screw head, on which or with which a rod can be secured and the two rods are connected to each other via a cross connecting device.
2. Prior Art
Osteosynthesis devices of the kind noted above are well known. They serve on the one hand to correct, stabilize, or stiffen bones. For example, German Patent 26 49 042 C2 discloses a shim, which rests upon the bone and is fixed by means of a bone screw. This bone screw is furthermore embodied as a retainer for a threaded rod, which serves as a correction rod. The force introduced into the bone via the threaded rod, the bone screw, and the shim is distributed onto the bone via the shim and effects a correction of the position of the bone. A bone corrected in this manner, though, requires stabilizing, which requires securing a further stabilizing element to the bone. This stabilizing element may, under some circumstances, have to be secured to another place on the bone, which makes a further operation necessary.
Further osteosynthesis devices are known from DE 31 21 271 C2, DE 39 16 198 A1, DE 41 10 002 C1, DE 41 07 480 A1, EP 443 892 A1, CH 672 420 A5, GB 2,178,323 A, CA 1,304,267 A, U.S. Pat. No. 5,030,220, DE 36 42 067 A1, EP 465 158 A2, EP 348 272 A1, and EP 346 521 A1. In the latter reference, it can clearly be seen that individual vertebrae of a spinal column are connected to one another via a number of bone screws and two rods. In this manner, the individual vertebrae can in fact be corrected, but not stabilized. Additional elements are required for stabilizing, which elements are disposed as lateral connectors between the two rods, as is known for example from EP 348 272 A1. Systems of this kind, however, are only partially suited to correct the positions of individual vertebrae, which as a rule, is carried out by pressing adjoining vertebrae against one another.
U.S. Pat. No. 4,289,123 discloses a device with which vertebrae can be displaced parallel via two threaded rods. With this device even a slight rotation of individual vertebrae is not possible. In addition a stabilizing of the vertebrae is only possible in part since they can move in the plane of the disks between vertebrae.